Can I Use Moisture Meter on Drywall?

We have a powder bath that often has a humid smell similar to damp hay. I have checked for leaks and bleached the toilet and sink drain but the smell persists. With a UV light I can see what looks to be a moist area on the ceiling which would indicate a leak from the tub above. By hand, I can't tell whether the ceiling is damp, or just cold. I do know that the putty around the drain had dried out two years ago which resulted in ceiling discoloration about four feet away in another room. I am beginning to wonder if the leak also traveled along the bottom of the tub or a joist.

Can I use a woodworking moisture meter to test drywall?

If so, can anyone recommend a model that you are also happy with in the shop?

Todd

You sure can. It's done all the time for insurance purposes after a flood.

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Originally Posted by Todd Willhoit

Can I use a woodworking moisture meter to test drywall?
If so, can anyone recommend a model that you are also happy with in the shop?

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Jason didn't mention if his meter was a pin or pinless type.

I use a pinless Wagner meter for wood, model 220 I think. I have not tried it on anything but wood, although it reports a lot of moisture in my hand when I'm turning it on. :)

These meters rely on the density of the wood and must be set to the proper number for each species. It would be easy enough to slide along the drywall and see if the reading changed in the suspected spot.

But trying to think of the unknowns here, for example would drywall behave like wood or might something confuse the meter? Could some chemical process cause wet drywall or wet then dried drywall to confuse the pinless meter? I don't think so but who knows.

If I wanted to try it on drywall I would get two small pieces of scrap drywall and get one wet. Check both of those with the meter then let the second one dry out and check it again. Or try asking Wagner - they probably have been asked this before.

Regardless, the pinless meter is a great tool to have in the shop. I process a lot of green wood and air dry for turning blanks.

JKJ

Lignomat, which makes moisture meters for wood, also has versions explicitly for drywall. For instance http://www.lignomatusa.com/meters/li...isture-bamboo/ One interesting thing is that the measurement range for drywall on this device is 0-2%. I'm not sure a wood moisture meter would reach down that low.

Thanks guys. Is there any preference for pin v. pinless?

Wagner MMC220, 5-32%, $395 (Huge ouch!)
Lignomat Mini-Ligno S/D, 0-7.5% for gypsum, $110 (This might be the ticket.)

Jason, what meter do you use?

I didn't say I have a meter (I don't)--just that they do get used for drywall.

Lowes sells a pin moisture meter for $30
https://www.lowes.com/pd/General-Too...-Meter/3136919
And a Pinless version for $40
https://www.lowes.com/pd/General-Too...Meter/50284821

They both have drywall scales on them... and wood scales
Have the pin version and it works pretty good... It is close to the Delmhorst & Wagner meters I have...

Many thanks guys for the excellent input. Lowes is nearby and the price is right. I'll give it a shot.

One more little tip--a pinless meter can be used as a meter with pins--just drive two small nails into the item to be measured and touch the electrodes to the nails.

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Originally Posted by Todd Willhoit

Many thanks guys for the excellent input. Lowes is nearby and the price is right. I'll give it a shot.

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Todd, please let us know what you think of it. The (few) reviews are not very favorable.
edit: I am referring to the pinless reviews

Jason,
I like that idea, but it looks like this pinless meter uses a large rectangular pad on the back and RF energy to make a measurement.

Rick,
I noticed that too and it had me leaning toward the pin version.

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Originally Posted by Todd Willhoit

Jason,
I like that idea, but it looks like this pinless meter uses a large rectangular pad on the back and RF energy to make a measurement.

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The Wagner pinless meter I use works exactly that way - there are no electrodes or contacts. The rectangular pad does need to be in contact with a flat surface of the wood which makes it good for boards but not useful on a curved surface such as the side of a rough-turned bowl. Perfect for lumber.

The flat surface also should be as least as large as the rectangular pad. I think it detects moisture about 3/4" down from the surface. I use the Wagner a lot on turning blanks, checking from several sides of blocks. The numbers usually vary a bit on different sides but it gives me a good idea if the blank is dry enough to turn.

i suspect the cheap pinless version would show you if drywall was wet or dry but probably not give an accurate moisture content reading. Testing on two small pieces of drywall, one moistened and one dry, would let you know if it was going to work in your ceiling.

JKJ